SEPARATION OF ZINC DIALKYLDITHIOPHOSPHATES IN LUBRICATING OIL ADDITIVES BY NORMAL-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Eleven zinc dialkyldithiophosphates have been synthesised and their mi xtures separated by normal-phase HPLC on a 5-mu m silica column. Dichl oromethane or heptane-based eluents containing alkylamine (less than o r equal to 0.4%) and acetic acid in a volume ratio of 2:1 and 1% metha nol were suitable for separation of mixtures of these metal complexes in commercial lubricating oil additives. In all cases tested, the zinc complexes eluted from the column without decomposition and there was no evidence for ligand-exchange reactions having taken place during sy nthesis or on the column.